In traditional time domain reflectrometry (TDR) systems, the length of, or the location of a fault or a discontinuity in, a wire cable can be determined by transmitting an electrical launch pulse down the length of the cable. Any change in the characteristic impedance of the transmission medium, i.e. the wire cable, will result in a reflection of the electronic pulse. A discontinuity can be caused by, for example, a change in the gauge of the medium, open termination of the medium, shorted termination of the medium, a load coil, a bridged tap, or splice faults in the medium. A bridged tap event is defined as a shorted event followed by an open event. Accordingly, upon reaching the end of the cable, or upon reaching the location of a fault or a discontinuity, the transmitted electronic pulse is reflected. The transmitted electronic pulse returns down the length of the cable to the point of origin.
A reflection of the transmitted pulse is also called an event. There might be multiple events associated with a single launch pulse. Since the velocity of propagation of the electronic launch pulse in the transmission media, e.g. wire cable, is known, the distance to the cable end, or to the fault location, may be precisely determined by measuring the time between the transmission of the electronic pulse and the return of the pulse reflection. Generally, the time between a launch pulse to an event represents twice the distance to the location of the discontinuity.
Methods of using peak detection to identify an event and to the associated location of the event are known. Special hardware is typically used to produce an optimum launch pulse. Typically, the transmitted launch pulse is narrow, however, various drawbacks are associated with narrow launch pulses. Reflections of narrow launch pulses are highly attenuated and relative noise is high. On longer loops, the reflections associated with the events have small signal to noise ratio and short reach, making the reflections difficult to detect.
While wider launch pulses may be used, these are accompanied by a host of other drawbacks. The falling edge of a wider launch pulse will tend to smear and interfere with the reflected pulse, again making the reflections difficult to detect. It is typically difficult to eliminate this smearing effect in hardware, and the smearing is also hardware dependent. It has been a challenge to find effective solutions to isolate the reflected pulse from the smearing due to the falling edge of the launch pulse.
To this end, a consistent method for processing and interpretation of TDR signals is needed.